1. Field of Invention
The Emerging Field of Computer Telecommunications Networking
Telecommunications means communication over a distance (tele means "far off" in Greek), and refers mainly to electronic forms such as radio, television, telegraph, telephone, facsimile ("fax"), and computer communications. In modern distance-applications of telecommunications, typically the message is encoded on the energy form (electrical, electromagnetic, or optical) that links the source and destination. In the 1980s and '90s, telecommunications has come increasingly to refer to systems that simultaneously accommodate voice, sound, text, graphic, image, computational, and moving-image message forms. This invention supports improved telecommunications networking between computers and between peripheral devices that are connected to host computers.
Computer Communications
Since the 1960s, computer design has included the development of systems for the remote linkage of users to computers (time-sharing), and of computers to one another. Networks that have arisen for military, government, and large-company commercial users evolved beginning in the 1970s in Western Europe, Japan, and the United States. These networks have become increasingly interconnected and have included new additions from other regions of the world. In the 1990s, with large increases in the numbers of desktop computers on these networks, and further connections over the public telephone networks, it has become possible to exchange messages (electronic mail, or e-mail), computer bulletin-board postings, information files, and computer programs with thousands of other computers in the same network.
Among the best known noncommercial computer networks is the Internet which, in the early 1990s, connected some 13 million users worldwide. In many respects, the Internet offers a preview of computer-based public telecommunications of the future.
By the mid-1990s, up to 150 million personal computers had been connected to networks, as estimated by respected industry analysts. The vast majority of these networks involve the use of Unshielded Twisted Pair (UTP) or Shielded Twisted Pair (STP) wiring.
As implied in the earlier discussion of digital coding, it is technologically possible to combine nearly all telecommunications services on a common, very-high-capacity, switched, and interactive network. Video, voice, graphics, data, and computation services could all be easily and inexpensively available over this "information highway"--which would involve an interlinking and upgrading of already existing systems.
Just as the growth of industrial and urban society has depended upon such infrastructure components as transportation facilities and water and power supply, scholars of modern growth and development see telecommunications, and its computer capabilities, as a major infrastructure component of the information age. The economic development policy of the administration of President Bill Clinton included the development of the information highway as a basis for encouraging new businesses and improving the delivery of educational and social services. The future will see much more telecommunications planning in the form of infrastructure development.
Basic Components
The basic components of a telecommunications system are usually identified as the devices that link source and destination: (e.g., transmitter, signal, medium, and receiver); noise that may interfere with this process; and feedback that represents a reversal of message flow. Source and destination are defined as any entities--people or machines--capable of creating or responding to messages. A source selects a message, which is converted by a transmitter into an energy form, or signal, that can travel by a medium, usually broadcasting or wire, to a receiver that converts the message back to a form that can be understood by the destination. Several factors contribute to a loss or distortion of the signal. Collectively they may be referred to as noise; however, such effects as external interference (common-mode interference), inter-symbol interference, jitter, cross-talk (especially so-called near-end cross-talk), and attenuation all contribute to lowered usability of the signal once it has traversed a length of a given transmission medium.
Computer and Peripheral Networking
Within a network, the source and destination are each referred to as a node. In a computer network, the node is a host computer that interfaces with the human user(s) and with other host computers by means of said network. The computer is called a host because it serves as the center of a computing system. Peripheral devices such as disk drives, CD-ROMs, tape drives, printers and the like are networked together to form a system. A peripheral device may be connected to more than one host computer allowing the sharing of its resources.
Networking Media
Both the host computer node and the networked peripheral require a plurality of pairs of conductive connections to accomplish transmission at the Physical Layer. These can include Shielded Twisted Pair (STP), Coaxial Cable, and Unshielded Twisted Pair (UTP). Optical cables can also be used, with the required optical interfaces and connectors, in place of metallic or other electrically conductive media. Most modern office buildings have Unshielded Twisted Pair (UTP) wiring laid within walls and in ceilings. It has been estimated that over 90% of the in-place wiring is UTP. In earlier implementations of networks, STP constituted a greater share of the installed base of copper cabling. In the opinion of some cabling infrastructure suppliers, with the use of higher and higher communication speeds, and in situations where interference constraints or problems with compliance with FCC requirements are acute, there may well be a resurgence in the use of higher quality STP cabling.
Signal Protocols
A variety of protocols are used for host computer node and peripheral networking, including Carrier Sense Multiple Access with Collision Detection (CSMA/CD), often referred to as Ethernet, Token Ring, Distributed Queue Dual Bus (DQDB/SMDA), Asynchronous Transfer Mode (ATM), or Fiber Distributed Data Interface (FDDI), Small Computer (SCSI), Serial Storage Architecture (SSA), and Fiber Channel. Of these SSA is developing technology based upon a set of ANSI standards.
2. Description of Prior Art
Transmission Media
Various networking protocols, including Token Ring, Distributed Queue Dual Bus (DQDB/SMDA), Asynchronous Transfer Mode (ATM), or Fiber Distributed Data Interface (FDDI), Small Computer (SCSI), Serial Storage Architecture (SSA), and Fiber Channel expect, at least, Shielded Twisted Pair (STP) cabling.
Simple Shielded Twisted Pair (STP) cabling consists of a twisted pair or a multiplicity of twisted pairs, over which a single conductive shield is wrapped.
Higher-quality Shielded Twisted Pair (STP) consists of either multiple twisted pairs of wires in a single cable within which each pair is surrounded by a conductive shield, or a multiplicity of individually shielded twisted pairs, which themselves together are overwrapped with a conductive shield. These cables work well at high transmission speeds (up to 300 megabaud and beyond).
Unshielded Twisted Pair (UTP), sometimes called Telephone Twisted Pair, consists of one or more pairs of two wires held together by twisting them and insulated by, usually, a type of plastic. Different pairs within a cable will often be twisted using different numbers of twists per unit of cable length. While Unshielded Twisted Pair is the most prevalent installed wiring, it can have significant limitations The transmission characteristics of the wire itself are impacted by the presence and effect of non-ideal and non-linear properties such as impedance (a combination of resistance, inductance, and capacitance) in the cable and the associated connectors. The higher the frequency of the signal, the more that it will be attenuated, that is, the intensity of the desired high frequency signal components will be reduced. The higher frequency components of the signal, are more prone to contribute to unwanted interference in adjacent wire pairs in the cable (cross-talk). Electromagnetic coupling to the external environment also limits the transmission capacity and suitability of UTP. To get UTP to handle data at the high speeds needed for modern host computer and peripheral networking, a more complex approach is needed.
Adaptive equalization, as used in this invention, has been used to allow the use of unshielded twisted pair cabling within a slow-speed 16 Mbits/second Token Ring network. This is described in U.S. Pat. No. 5,455,843. The token Ring network protocol is significantly different from the buffer-insertion based protocol being enhanced by this invention. Also, the 200 and 400 Mbits speeds, discussed herein, are from 12.5 to 25 times faster, thus permitting the bandwidth required by today's and tomorrow's bandwidth intensive systems.
Another approach used to enable the use of unshielded twisted pair cabling is to demultiplex the signal into multiple data channels, as show by U.S. Pat. No. 5,119,402. The invention, discussed herein, does not use demultiplexing and does not use multiple channels, and the speeds attained by this invention exceed the maximum 125 megabits per seconds mentioned in the Ginzburg patent. Also, the Ginzberg patent mentions Fiber Distributed Data Interface technology used with Token Ring as opposed to the buffer insertion-based protocol. A second Ginzberg patent (U.S. Pat. No. 5,408,500) uses a duobinary coding system and does not use adaptive equalization.
The use of adaptive equalization with unshielded twisted pair wiring is not new (U.S. Pat. Nos. 4,424,498 and 4,650,930), the equalizer used in the present invention is improved along with the improved circuitry needed to handle buffer inserion-based protocol at much higher speeds than envisioned in the 1980's.
Computer and Peripheral Networking Protocol
Buffer Insertion is one approach to Computer and Peripheral Networking, wherein nodes within the network utilize a buffer to ensure that the network is deadlock free. A double ring approach is used with no tokens. The status of the insertion buffer governs node transmission. If nothing is currently being received into the insertion buffer and the insertion buffer is empty, then the node may transmit. This is described in part in Patent Cooperation Treaty Application WO 92/10894.
When a node receives anything from upstream it checks the address in the frame header to determine if it is the destination of the message. If the frame is addressed to this node then the data is directed to the node's receive buffer and does not go into the insertion buffer. This routing scheme is described in part in UK Patent Application GB 2 268 374 A. The serial data receiver approach used is described in U.S. Pat. No. 5,003,308. The standard Buffer Insertion approach uses an error recovery mechanism as described, in part, in UK Patent Application GB 2 268 373 A and GB 2 250 897 A.
A Disk Drive Synchronization used for disk drives utilizing the Buffer Insertion approach is described in European Patent Application 544 954 A1.
The standard Buffer Insertion approach fairness algorithm is described in U.S. Pat. No. 4,926,418.
The Buffer Insertion approach, as defined in the Serial Storage Architecture (SSA) ANSI standard, has an inherent switch level limitation. Therefore, a string or loop of nodes, that do not cross switches, is often an efficient architectural solution. Inherent to the string approach is the fact that an off-line non-operating node will break the string unless a bypass mechanism is utilized (the old-fashioned serial Christmas tree light problem).
The American National Standards Institute (ANSI) has published standards covering the Buffer Insertion approach to computer communications, and specifically the Serial Storage Architecture (SSA) method. These standards cover the specifications for the so-called Physical Layer, that is, the manner in which the physical connections between nodes are established and the nature of the electrical signaling that is used between them. For example, the published ANSI standard: ANSI X3.293-1996: Information Technology--Serial Storage Architecture--Physical Layer 1 (SSA-PH1) defines a single type of cable connection between physically separate nodes, using a cable connector available from a single manufacturing source, and employing two pairs of twisted wires for bi-directional communications, i.e. one pair in each direction, to and from each port on a node. The two pairs in the specified ANSI-standard Buffer-Insertion compliant simple STP cable are unshielded from each other, but are contained within a single outside conductive shield.
In addition, the SSA-PH1 standard defines the use of encoded data transmitted as a base-band digital signal using the non-return-to-zero (NRZ) method at 200 megabits per second.
The ANSI SSA-PH1 standard also refers to additional methods of connection that might be defined in a later standard, including optical links, and the use of higher communication speeds of 400 megabits per second using the base-band NRZ method. In fact, however, the later standard for the Physical Layer, SSA-PH2, now nearing completion of its public comment phase, defines the use of the same type of connector and simple STP cabling as SSA-PH1, and further, it stipulates that a device may be considered to comply with the SSA-PH2 standard even though it is capable of reliable communications over a distance of only 20 meters, while signaling at either 200 or 400 megabits per second.
In addition, SSA-PH2 explicitly excludes the detailed definition of devices called "Port Connection Couplers" (PCC's), that may be used to increase distances between nodes in a ANSI SSA-PH2 compliant network. Instead, PCC's are only required to comply with the SSA-PH2 signal quality and cable connections at the individual nodes. Between nodes, individual PCC's may include optical or other copper connections over longer distances than 20 meters, with suitable conversion to the ANSI compliant cable/connector combination at each node. The internal details of such PCC's including the manner of signaling between their elements, and the types of signal processing that is used are left to the manufacturer to define.